Some rotational atherectomy devices for removing plaque and clots that have accumulated on a blood vessel wall are known from the prior art. Relatively soft, cholesterol-rich atheromatous material often hardens into a calcified atherosclerotic plaque to restrict the flow of blood.
Several methods are currently available to form a channel through a blocked blood vessel. Initially, a guidewire is used to probe a channel through the blockage in the blood vessel in order to reach a downstream unblocked blood vessel portion. After the guidewire has been advanced through the blockage, a physician manually guides a catheter through an introducer sheath and over the guidewire to the atheroma site. For example, an angioplasty balloon catheter is passed over the guidewire and is inflated to dilate the blockage.
This method is known to succeed in soft or partial blockages of a blood vessel, through which the guidewire can be easily passed. It carries the risk, however, of causing tears in the arterial wall due to the diameter of the inflated balloon. Moreover, such methods do not remove the atheromatous material from the vessel.
Other methods use catheter devices having a rotating or vibrating tip operated by an external drive unit or power source, which is coupled to the tip by a flexible drive element, such as a cable, spring or shaft. Such devices such as disclosed in U.S. Pat. No. 6,818,002 are introduced into a blood vessel over a guidewire, and the atheroma or blood clot material is shaved from the wall of the artery, while risking perforation of the arterial wall, and may then be aspirated by the catheter out of the vessel in order to prevent distal embolization.
Such methods employing a guidewire to first probe a channel through the blockage in the blood vessel and then introducing the rotating or vibrating device over the guidewire to remove the atheroma are in less use because most physicians can treat the occluded vessel with a balloon or stent if the guidewire has already passed the occluded segment.
WO 2013/056262 discloses a rotational atherectomy device having a handle, a distal cutter assembly for cutting and capturing occlusive material, and a catheter extending between the handle and the cutter assembly. A motor housed within the handle causes a torque shaft connected to the cutter assembly to rotate concentrically. The outer diameter of the cutter assembly is greater than or equal to that of the catheter to maximize the overall cutting area. The reduced diameter of the catheter body reduces frictional contact with the vessel wall and also permits the injection of radiographic contrast material around the catheter body in the guide sheath.
This atherectomy device configuration has some deficiencies. Due to its relatively large dimensions, the cutter assembly has difficulty in penetrating the blockage when contacting the smooth and hardened plaque, and often slides towards the vessel wall in response to the encountered resistance to the removal of the occlusive material. Even if the prior art atherectomy device were successful somehow in initially penetrating the hardened plaque, it would have difficulty in forming an opening in the plaque since the rotating cutter assembly follows a concentric path with respect to the guidewire, and therefore is able to cut only that occlusive material coinciding with, or adjoining, the guidewire; if the occlusive material adjoining the guidewire is hardened, however, it generally cannot be penetrated. Additionally, the physician is not able to accurately visualize the location of the distal cutter assembly by means of the contrast material since the contrast material is injected between the catheter and the introducer sheath at a distance from the distal end.
Copending International Publication WO 2014/106847 by the same Applicant discloses an expandable atherectomy device, comprising a rotatably motor-driven flexible hollow shaft that is slidable over a guidewire introducible through a flexible catheter tube and is coaxial with the longitudinal axis of the guidewire, an expandable cutting unit connected to a distal end of the hollow shaft, and an actuator which is operable to induce selective expansion of the cutting unit. The hollow shaft comprises inner and outer tubular portions, which may be embodied by inner and outer cables and which are simultaneously rotatable while one of the inner and outer tubular portions slides over the other in a direction substantially parallel to the longitudinal axis. The cutting unit is expandable in response to an actuated action which causes two separated ends of the cutting unit to be brought closer together. The cutting unit, when expanded, is eccentrically rotatable about the longitudinal axis to cut and remove atheromous material from a blood vessel.
Although this atherectomy device is very effective in removing atheromous material and in being selectively introducible to both large and small sized blood vessels, several mechanical difficulties have been found:
1. As result of the compression force applied to the hollow shaft that causes the two ends of the cutting unit to be brought closer together, the coils of the outer cable tend to expand and to be separated from each other. The outer diameter of the cable becomes enlarged, increasing the frictional force with a plastic tube into which removed atheromous material is drawn and shortening the total length of the hollow shaft.
2. Although the proximally located actuator allows relative linear movement and simultaneous rotation of the inner and outer tubular portions, the hollow shaft is not provided with a mechanism at its distal end to assure uniform rotation of the inner and the outer portions. Without such a mechanism, the cutting unit is subject to failure.
3. The angle of the cutting unit made by the coils of the external cable must be optimized to reduce force and fatigue at the bending points, and to assure maximum of flexibility and strength of these coils in close and open conditions. Moreover, if the external cable is made of memory metal (Nitinol) and the internal cable is made of stainless steel, it is extremely difficult to weld the two metal compositions together. More importantly, welding of Nitinol creates a local thermal effect that weakens the material and increase the possibility to break at the weld zone.
4. The physician generally needs to inject contrast material after the removal of atheroma from a blood vessel, to determine if the treated vessel is now unoccluded and to verify that no damage was made to the blood vessel wall. In order to do this, the atherectomy catheter must be removed, and replaced by another catheter to be introduced to the atheroma site over the guidewire. This requires time, especially if the atheroma is not fully removed and an additional operation with the atherectomy catheter is required.
It is an object of the present invention to provide a rotatable atherectomy device that is assured of penetrating hardened plaque within a blood vessel without risking perforation of the blood vessel wall.
It is an additional object of the present invention to provide a rotatable atherectomy device that is capable of cutting occlusive material which does not adjoin the guidewire over which the catheter is introduced into the blood vessel.
It is an additional object of the present invention to provide a rotatable atherectomy device that is not dependent upon a guidewire that first probes a channel through the blockage.
It is an additional object of the present invention to provide an atherectomy device that facilitates the accurate visualization of its distal end by means of contrast material, and without requiring separate catheters for an atheroma removing operation and for injection of contrast material.
It is yet an additional object of the present invention to provide, in one embodiment, an atherectomy device having an expandable cutting unit and a hollow shaft consisting of coaxial inner and outer cables arranged such that the coils of the outer cable will remain in abutting relation with each other and in a substantially uniform shape and diameter.
Other objects and advantages of the invention will become apparent as the description proceeds.